This invention relates to a power operating system for a vehicle liftgate that is pivotally attached to a vehicle compartment for pivotal movement about a hinge axis that in normal orientation extends horizontally, and more particularly to a power operating system that will move such a liftgate from and between fully closed and fully open positions.
Utility vehicles, vans and station wagons with rear liftgates that are hinged at the top about a generally horizontal axis are used by large numbers of people today. Some of these liftgates are large and heavy, thus making them difficult to open and close. Some of the liftgates also reach a great distance above the ground when they are fully opened, thereby making them very difficult for people of shorter height to close. For these and other reasons many people would like to have a power operating system for opening and closing the liftgate.
A number of different liftgate openers have been tried in recent years. Some of these liftgate openers have a single cable that opens and closes a liftgate in connection with a counterbalance system, such as a gas spring counterbalance system. Liftgates and similar hinged body panels that are provided with a single cable opener and closer are generally lightweight and have a relatively small range of movement, such as trunk lids. Moreover, gas spring output varies with temperature. This complicates power liftgate systems that rely on gas springs to assist in opening the liftgate. The gas spring or springs must be strong enough to open the liftgate on the coldest day (xe2x88x9240xc2x0 C.). This results in gas springs that increase closing resistance substantially on the hottest day (80xc2x0 C.). Therefore, a very large electric motor must be used to close the liftgate.
Liftgates that have two or more gas springs for a counterbalance system are common. These gas springs generally occupy a position in which their axis is substantially parallel to the liftgate so that the gas springs are hidden when the liftgate is closed. In this closed position the moment arm of the gas springs is quite small. With such systems the liftgate may move about one-third of its total travel range before the gas cylinders exert sufficient force to open a liftgate further without the application of an independent lifting force. There are even some systems in which the gas springs pass over center and bias a liftgate toward a closed position when the liftgate is closed. With these self-closing systems a liftgate may need to be more than one-third open before the gas springs will open the liftgate further.
The force required to hold a liftgate in a given position along its path of movement from a closed position to a fully open position varies substantially in some liftgate opening systems. A power liftgate closer must exert sufficient force to hold a liftgate in any given position along the path of movement, plus the force to overcome friction, and plus the force required to accelerate the liftgate during liftgate closing. If the total force exerted by the liftgate power closure varies substantially from one position between fully opened and closed to another position between fully opened and closed, it may be difficult for the control system to detect an obstruction and stop the liftgate without incurring damage to the vehicle or to the object that obstructs the liftgate.
It is also important that a liftgate opener have as few stationary and moving parts as possible and be a compact design in order to provide minimum obstruction to the cargo opening closed by the liftgate. The liftgate power operating system also should be operable to allow the liftgate to be moved manually, even when equipped with a power operated liftgate system, and should be usable alone (uncounterbalanced) and in conjunction with a liftgate counterbalancing system.
Accordingly, among the objects of the present invention are to provide an improved vehicle liftgate power operating system that can be remotely controlled and electrically powered to move the associated liftgate from and between fully closed and fully open positions, usable in conjunction with a counterbalance system, electrically powered and capable of remote control, such as by the vehicle ECU unit, that is compact, rugged, requires a minimum of moving and stationary parts, economical to manufacture and maintain, easier to package than prior systems and provides better clearance with the vehicle head envelope than prior systems, lighter in weight, which is easily sealed against intrusion by car wash and rain water and against expulsion of lubricant contained in the liftgate power operating mechanism, which can be employed with single or dual output shaft electric motors, and that overcomes the aforementioned as well as other disadvantages of the prior art.
In general, and by way of summary description and not by way of limitation, the invention accomplishes one or more of the foregoing objects by providing an improved vehicle liftgate power operating system wherein an arcuate"" clam shell type housing movably encases a curved rack gear subassembly of complemental curvature to the housing and that is movable bodily endwise therein and protrudes at one end from an end opening of the housing so as to also function as a drive link that is pivotally coupled to the liftgate. Preferably a pair of curved runner bars flank the rack gear and are fixed thereto and protrude therebeyond for coupling by a clevis pin and clevis bracket to provide the pivotal coupling of the rack gear subassembly to the liftgate. The housing is pivotally coupled to a hinge bracket that mounts the housing to the vehicle so that the entire housing can swivel about the mounting pivot connection.
In one embodiment, an electric motor is directly mounted to the side of one of the housing half-shell parts and has a drive shaft that extends into the housing and is coupled in driving relation to a pinion gear disposed in constant mesh with the teeth of the curved rack. The rack subassembly is movably roller-supported within the housing by runner wheels attached to the rear ends of runner bars that track in the housing and by riding on a wheel mounted interiorly on the housing near its exit end. Dual hubs on the pinion gear overlie the smaller radius edges of the runner bars such that, in cooperation with the roller engagement of the runners within the housing, the rack is accurately maintained in any travel position during its bodily motion relative to the housing, the appropriate constant mesh tooth engagement is maintained between the pinion and rack during operation, and frictional resistance in the drive mechanism is substantially reduced. The pivotal mounting of the housing on the vehicle helps compensate for vehicle liftgate/body hinge mount assembly tolerance variations. The curvature of the housing and associated rack gear subassembly is uniform about a common center of curvature which in turn is coincident with the pivot axis of the liftgate-hinge. Thus insures a constant 1:1 ratio in the drive linkage action throughout operational travel of the rack gear subassembly in operating the liftgate between its fully closed and fully open positions.
In a second and preferred embodiment of the invention also disclosed herein, the clam shell housing is modified to provide a motor mounting bracket portion at the exit end of the housing, and the rack gear is provided with gear teeth on its larger diameter lower edge, rather than on its smaller diameter upper edge as in the first embodiment. The pinion gear is directly mounted on the output shaft of the motor drive unit, and again is in constant mesh with the gear teeth of the rack. A pair of rollers are mounted in the motor mounting bracket portion of the housing and rotatably engage, support and guide the radially opposite inner and outer edges of the runners that flank the rack gear. The curved housing track, on which runs the roller journaled at the rear end of the rack subassembly, is formed as a laterally outwardly protruding embossment on each housing half-shell. The surrounding peripheral marginal portion of each housing half-shell lies in a plane offset from the plane of the embossment and is provided with mounting bosses for receiving housing fasteners and for journal attachment of the housing swivel bracket subassembly. Preferably the motor drive unit is right angle drive type having an electromagnetically operated clutch transmission mounted to the motor unit so that the motor extends compactly alongside the housing.